A carpet in a vehicle is usually fixed on a floor of the vehicle by a plurality of fasteners to avoid undesired impact on other vehicle parts such as a braking pedal and accelerating pedal due to movements of the carpet. Conventionally, the carpet is fixed on the floor by a bolt and nut connection. For example, a threaded bolt is welded on the floor and a carpet with a hole is placed on the floor to make the bolt pass the hole. Then, a threaded nut is connected with the bolt and the threaded nut presses on the floor to secure the carpet on the floor. Because the bolts on the floor of different vehicles have variable diameters, different nuts are required to match with the bolts. During the assembling process of the carpet, it is possible to mount an unmatched nut to the bolt, thus mounting error may be caused. If an operator selects a nut with a relative smaller inner diameter to mount on a bolt with a relative larger diameter, he or she may need to replace this nut with a correct one, which increases the mounting time. U.S. Pat. No. 7,891,151B2 discloses two-clip tubular fastener used to clamp a sheet-like member between flanges of the clips. The flanges of the fasteners exert a predetermined clamping force on an undercover while permitting planar movement of the undercover. One of the flanges has a configuration that engages a co-operable configuration on the undercover to prevent undesired turning of a first clip relative to a second clip. However, this kind of fastener has a complicated structure and low fastening strength. There is a need for a fastener with a simple structure, strong fastening strength, and suitable for the bolts having different diameters.